Timekeeping in Astronomy

"Captian's log, stardate 1513.1. Our position: Orbiting planet M-113. Onboard the Enterprise: Mr. Spock temporarily in command. On the planet: the ruins of an ancient and long dead civilization. Ship surgeon McCoy and myself are now beaming down to the planet's surface. Our mission: routine medical examination of archaeologist Robert Crater and his wife, Nancy. Routine, but for the fact that Nancy Crater is that one woman in Dr. McCoy's past."

 - Opening of Star Trek: The Original Series, Season 1, Episode 1; "The Man Trap"

If you're curious like me, you'd have noticed that the Captain's log from Star Trek used some form of strange new system of measuring time. What does stardate 1513.1 represent? It turns out, it doesn't really mean much. It was just another way of making the show look futuristic. From Wikipedia:

"We invented "Stardate" to avoid continually mentioning Star Trek's century (actually, about two hundred years from now), and getting into arguments about whether this or that would have developed by then. Pick any combination of four numbers plus a percentage point and use it as your story's stardate."

But interestingly, the convention used by astronomers to keep time is very similar sounding to the stardate system seen in Star Trek. Astronomers use what is called a Julian Date whenever the time and date of a measurement needs to be mentioned.

Calendars have a long and messy history. The calendar system that is in use around the world today is called the Gregorian Calendar. People only started using this calendar in the late 1500s. Before that there was something called the Julian Calendar which was introduced by Julius Caesar in 45 BC. These are two big calendars. But there were also a lot of other calendars in use by different countries and cultures. A look at calendar systems in wikipedia shows a mind boggling and confusing list of widely varying systems. Some are similar, some are wildly incompatible. Also, due to the fact that the time taken by the earth to go around the sun is not an exact integer multiple of a day, errors inevitably arise when measuring time in years or months. Astronomers needed a standardized method of referring to time for astronomical observations. This was the motivation behind the adoption of the Julian Date.

A Julian Day Number is an integer that represents the number of days that have passed since 1st January 4713 BC in the proleptic Julian Calendar or 24th November 4714 BC in the proleptic Gregorian Calendar. (NOTE: A preleptic calendar is a calendar obtained by extending a calendar system backwards in time to date before AD 4)

The Julian Date of any point in time is the Julian Day Number of the previous day along with a decimal number that represents the fraction of the next day that has passed.

For example, the 1st of January, 2014 1800 hrs is represented by a Julian Date of $2456659.25$

I hope everyone has a wonderful time celebrating another complete revolution of the Earth around the Sun. An exciting year lies ahead!

Richard Feynman on Education

Feynman, a robust and awe-inspiring physicist who won the Nobel Prize for his work on Quantum Electrodynamics, once went as a visiting Professor to one of the universities in Rio, Brazil. He was able to get an inside view of how the system worked there, and with characteristic wit delivers a talk pointing to the many flaws - the over emphasis on memorization, the lack of emphasis on actual hands on experience and empirical evidence, and how the system is loaded against the people who truly do have an idea of what it means to be a scientist - and how they sadly end up discouraged and instead conform to the prevailing "wisdom". In the following excerpt from "Surely You're Joking, Mr. Feynman!", he gives a first hand account of how the event transpired and eventually ended.

---

In regard to education in Brazil, I had a very interesting experience. I was teaching a group of students who would ultimately become teachers, since at that time there were not many opportunities in Brazil for a highly trained person in science. These students had already had many courses, and this was to be their most advanced course in electricity and magnetism – Maxwell’s equations, and so on.

The university was located in various office buildings throughout the city, and the course I taught met in a building which overlooked the bay.

I discovered a very strange phenomenon: I could ask a question, which the students would answer immediately. But the next time I would ask the question – the same subject, and the same question, as far as I could tell – they couldn’t answer it at all! For instance, one time I was talking about polarized light, and I gave them all some strips of polaroid.

Polaroid passes only light whose electric vector is in a certain direction, so I explained how you could tell which way the light is polarized from whether the polaroid is dark or light.

We first took two strips of polaroid and rotated them until they let the most light through. From doing that we could tell that the two strips were now admitting light polarized in the same direction – what passed through one piece of polaroid could also pass through the other. But then I asked them how one could tell the absolute direction of polarization, for a single piece of polaroid.

They hadn’t any idea.

The Beginner's Guide to the Galaxy

So you're interested in space and you're bored of watching documentaries on Nat Geo or the Discovery Channel. And you want something to do during the power cuts. Don't panic, here's our beginner's guide to astronomy.

So, shall we take that telescope?
Not so fast! That's one misconception that many people have. You don't need to have a telescope to begin astronomy. I'm not kidding. The sky is a calendar and there is so much you can learn with just limited tools! Once you're familiar with spotting basics objects like planets, Orion nebula and constellations, you can buy binoculars and telescopes. if you have a good budget, go for buying good quality "reflective" telescopes.

Now what?
There's tons of stuff that you can see with your eyes - satellites, planets like Mars, Jupiter, Venus, Saturn; the ISS (the international space station), the Pleiades star cluster (a...cluster of stars, duh), meteors and even the Orion Nebula (A collection of gas visible to the naked eye) . Stellarium is a good software that will help you find these objects () If you have an android, download Google sky map.

Start out getting familiar with the sky. First try to notice a very prominent constellation like Ursa Major or Orion the Hunter. You'll realize that most constellations barely resemble what they're supposed to represent :/ After that, it should be easy to spot the other objects using relative positions.

www.heavens-above.com will help you to spot satellites and the ISS, just make sure you set the home location to Trichy or Wherever You Live Town. Many 'iridium flares'  - bright reflections from a certain type of satellite - would be visible during the evening, it is quite fun to watch them swimming slowly across the sky. Once you have registered and entered your location, you can click the links for iridium flares and the ISS to see when they are visible.

Cool machi! What's next?
Just have an open mind. Remember, we're all amateurs here when it comes to the Universe. Expand your knowledge and try to understand what the stuff really means and absorb all the vastness and beauty. As the astronomer Carl Sagan once said, "Somewhere, something incredible is waiting to be known." His book and TV series, Cosmos is also a must watch, along with practically anything by Neil DeGrasse Tyson.The Bad astronomy blog  is a good place to check out recent developments in astronomy.

Glossary:
Magnitude: Scale used to measure brightness of celestial objects. It's a log scale, like the pH scale. Bizzarely, the lower the magnitude, the brighter the object is. Venus, the third brightest in the sky has a magnitude of about -4 or thereabouts, whereas a star with mag 5.5 is just visible to the naked eye. Stars with higher magnitudes are dim and can only be seen through telescopes or other devices.
Altitude: Angle of elevation in the sky, with ground level at 0 and zenith at 90 degrees. the Pole Star's alt is about 10 degrees in Trichy.
Azimuth: The direction of the object, with north at zero, east at 90, south-east at 135 degrees and so on.

Have a good journey!

Image Processing in Astronomy

"Having finished chopping up his roots, Harry bent low over his book again. It was really very  irritating, having to try and decipher the directions under all the stupid scribbles of the previous owner, who for some reason had taken issue with the order to cut up the Sopophorous Bean and had written in the alternative instruction:

Crush with flat side of silver dagger, releases juice better than cutting.

......(several sentences later).......

Harry crushed his bean with the flat side of the dagger. To his astonishment, it immediately exuded so much juice he was amazed the shriveled bean could have held it all. "

-J.K Rowling in Harry Potter and the Half Blood Prince

Basic sciences like physics have come so far that huge, monstrous, expensive beasts like the Large Hadron Collider are required to push the boundaries of scientific knowledge. The days were the lone astronomer spent long, peaceful hours staring through the objective lens in the remarkable solitude of the mountains are long gone. Today, very little astronomy is done by people physically looking through the telescope. Instead, we have gigantic tubes (or conduits to the cosmos as Neil deGrasse Tyson puts it) and state of the art, cryogenically cooled sensors take the place of the human eye. These sensors are hundreds of times more sensitive and quite a bit less prone to error and fatigue than the human eye.

In astronomy, the raw data we get from the telescope is Harry's Sopophorous Bean and and the flat side of the silver dagger represents the various image processing techniques and algorithms astronomers have in their arsenal. These algorithms and techniques can often make the data exude such a surprising amount of information that you'd be amazed that the weird looking stream of numbers could have held it all. Image processing is used in most parts of astronomy today. From basic observations of pulsars to extremely complicated things like radio interferometry image processing is a ubiquitous tool in astronomy. It is what is used to turn the grainy, ugly raw data we get from telescopes into the enchantingly beautiful images of the cosmos that people use as desktop wallpapers.

In this post I'm going to talk a bit about an image processing algorithm known as DRIZZLE. The DRIZZLE algorithm is special because it can be used quite easily by amateur astronomers to get good looking photographs of celestial objects.

The algorithm was developed by Andrew Fruchter and Richard Hook and is used when the low resolution of the CCD sensor results in the image being undersampled. The algorithm takes several images of the same portion of the sky with slight shifts applied to telescope aligns the stars to account for the shift and adds all the images together. This combined image has more information that any of the individual images and can result in a final image that seems to have a higher resolution than the actual sensor resolution. It's a bit like human vision. What your left eye sees is almost exactly the same as what your right eye sees except for a slight shift. Your brain is able to combine these two shifted images together to get information about depth which cannot be obtained from either of the individual images.

Here is an image from Wikipedia that shows the difference between a raw image and an image produced by using the DRIZZLE algorithm.

On the left a single 2400s F814W WF2 image taken from the HST archive. On the right, the drizzled combination of twelve such images, each taken at a different dither position.

If you're interested in learning more about Drizzle, you can go to this website. It has a more detailed but still accessible explanation of $DRIZZLE$ with more examples to help you visualize how the algorithm does what it does.

This is just the tip of the iceberg when it comes to image processing. I'll be blogging about more awesome image processing stuff over the next couple of years.

Until next time! :)